p-Phenylenediamines are important compounds (intermediates) for use as materials for dyes, pigments, polymers and agricultural chemicals.
Phenylenediamines can be prepared by various conventional processes. For instance, as disclosed in Japanese Patent Application Laid-Open (KOKAI) No. 51-26826 (1976), o-phenylenediamine can be prepared by hydrogenation of o-nitroaniline. This process, however, involves a reaction under a high pressure and, therefore, requires special equipment and an intricate operation for separating a catalyst.
Besides, as described on page 261 of BIOS FINAL REPORT 1153, nitroaniline can be reduced by an aqueous sodium sulfide solution to phenylenediamine. However, this process has the problem that large amounts of alkaline sulfur compounds are by-produced.
Also, it is possible to reduce p-nitroaniline by iron powder to obtain p-phenylenediamine, as described in PB 85172, but this process involves difficulties in separation of the p-phenylenediamine from by-produced iron compounds and in disposal of the iron compounds by-produced in large amounts.
As disclosed in Japanese Patent Application Laid-Open (KOKAI) No. 54-59237 (1979), furthermore, p-phenylenediamine can also be obtained by reducing p-nitroaniline by hydrazine by use of an iron oxide or iron hydroxide catalyst, however, this process necessitates troublesome operations such as separation of the catalyst used.
It is further known to obtain aminoanthraquinones by reacting nitroanthraquinones with hydrazine, as disclosed in Japanese Patent Application Laid-Open (KOKAI) No. 50-25555 (1975). It has not been known, however, to reduce other nitro compounds by hydrazine in the presence of an aromatic quinone compound or an aromatic dihydroxy compound as a catalyst, as in a process according to the present invention.
The conventional processes thus have the drawbacks of the intricate operation for separating the catalyst, the disposal of needless substances which are by-produced in large amounts, the necessity for a special apparatus, and so on.
The present invention provides an industrial process by which p-phenylenediamines can be prepared in a high yield and which is free from the above-mentioned problems.